Method of producing manganese dioxide

ABSTRACT

A method of producing manganese dioxide comprising the steps of pouring an aqueous solution of a soluble manganese salt and an aqueous solution of alkali carbonate into a reaction vessel and mixing the two solutions so that the two solutions may react with each other to produce manganese carbonate, heating the manganese carbonate produced in an atmosphere containing water vapor to produce crude manganese dioxide, and washing the crude manganese dioxide produced with dilute or concentrated nitric acid and then heating to produce manganese dioxide.

O J United States Patent [151 3,647,375 Tanabe 1 Mar. 7, 1972 [54]METHOD OF PRODUCING MANGANESE DIOXIDE Primary Examiner-Earl C. ThomasAssistant Examiner-Hoke S. Miller [72] Inventor. Isao Tanabe, Tokyo,Japan Atmmey McGlew and Tore" [73] Assignee: Japan Metals and ChemicalsCompany Limited, Tokyo, Japan [57] ABSTRACT Filed! 1959 A method ofproducing manganese dioxide comprising the 21 A L N S 868,644 steps ofpouring an aqueous solution of a soluble manganese 1 PP 0 salt and anaqueous solution of alkali carbonate into a reaction vessel and mixingthe two solutions so that the two solutions [52] US. Cl ..23/145 mayreact with h other to produce manganese carbonate, [51] "C013 45/02heating the manganese carbonate produced in an atmosphere [58] Fleld ofSearch ..23/l45 containing water vapor to p d crude manganese dioxideand washing the crude manganese dioxide produced with [56] Referencescued dilute or concentrated nitric acid and then heating to producemanganese dioxide.

UNlTED STATES PATENTS 1,275,666 8/1918 Ellisetal. ..23/145 3 Claims, NoDrawings METHOD OF PRODUCING MANGANESE DIOXIDE The present inventionrelates to methods of producing manganese dioxide. More particularly,the invention deals with a method of producing manganese dioxide of highquality and high efficiency which has particular utility in applicationin dry cells.

Manganese dioxide is used as a depolarizer for dry cells. In one methodof producing manganese dioxide known in the art, an aqueous solution ofa soluble manganese salt is produced from manganese ores by extractionwith acid and purification. An alkali carbonate is added to said aqueoussolution to produce manganese carbonate which is then subjected topyrolysis and oxidation to produce crude manganese dioxide from which adivalent oxide of manganese is removed with concentrated sulfuric acid,with the'manganese dioxide being activated at the same time. Themanganese dioxide produced by this method is generally referred to aschemical manganese. Such a process is described in US. Pat. No.1,275,666.

The manganese dioxide produced by the conventional method describedabove has a disadvantage when it is used with dry cells. The manganesedioxide produced by this method is in fine particle form. This reducesthe amount of charge of manganese dioxide filled in the cells for a unitcapacity of the cells, so that the dry cells using the manganese dioxideproduced by the conventional method have a short service life.

The present invention obviates the aforementioned disadvantage ofmanganese dioxide produced by the conventional method described above.Accordingly, the invention has as its object the provision of a methodof producing manganese dioxide of high quality which is adapted for usewith dry cells to fill the cells with a charge of manganese bicarbonateof high density.

The present invention provides a method of producing manganese dioxidewhich is characterized by comprising the steps of (1) preparing anaqueous solution of a soluble manganese salt by extraction andpurification from manganese ores and preparing an aqueous solution ofalkali carbonate which is in a range of proportion of Na co zNaHCO of6:4 to :10 or (NH CO :Nl-I HCO of 9.6:0.4 to 0:10, said two aqueoussolutions being poured separately and simultaneously into a reactionvessel in amounts in which the proportion of said aqueous solution of asoluble manganese salt and said aqueous solution of alkali carbonate isin a range from 1:0.9 to 111.2 in chemical equivalent and graduallymixed by agitation at a crystal precipitation temperature ranging fromroom temperature to 90 C. so that the two aqueous solutions may reactwith each other to produce crude particles of manganese carbonate havinga high rate of charge density which are rather spherical in shape; (2)heating the manganese carbonate produced by the preceding step to 280 to400 C. in an atmosphere containing to 80 percent by volume of watervapor or at 300 to 450 C. in atmosphere air to produce crude manganesedioxide; and (3) causing the crude manganese dioxide produced by thepreceding step to be impregnated with dilute or concentrated nitric acidin an amount which is 0.5 to 1.5 time as much as the divalent manganeseequivalent contained in said crude manganese dioxide, heating the sameat a temperature ranging from C. to the boiling point temperature ofnitric acid, and heating again to 160 to 300 C. to produce manganesedioxide, or treating with sulfuric acid crude manganese dioxide producedby the preceding step to produce manganese dioxide. The method ofproducing manganese dioxide provided by this invention which comprisesthe aforementioned three steps is capable of producing manganese dioxideof high MnO content, a high rate of charge density, and good dischargecharacteristics which is suitable for use with dry cells.

The steps of the method described above according to this invention willnow be explained in detail.

The aqueous solution of a soluble manganese salt used as a startingmaterial is generally an aqueous solution of manganese sulfate producedby extraction with sulfuric acid and purification from manganesecarbonate ores or reduced and roasted manganese ores. An aqueoussolution of manganese nitrate or manganese chloride may be used. It isonly by using an aqueous solution of alkali carbonate which is in arange of proportion of Na CO :NaHCO of 6:4 to 0:10 or (NH CO;, NH l-IC0of 9.6 0.4 to 0 10 that manganese carbonate having a high rate of chargedensity can be produced. It is only by processing the manganesecarbonate produced as aforementioned by the following step thatmanganese dioxide of interest which has a high rate of charge densitycan be produced. More specifically, the use of alkali carbonate of theaforementioned composition pennits the production of large and roundishcrystals of manganese dioxide of a diameter in a range from 40 to 100microns. The manganese dioxide produced as aforementioned has anapparent rate of charge density of 1.6 to 2.1 g./cc. (the apparent rateof charge density refers to a rate at which about 10 cubic centimetersof the dried sample is poured into a measuring cylinder with a capacityof 10 cubic centimeters and filling the same in said measuring cylinderby lightly tapping the bottom of the cylinder on a wooden plate). On theother hand, if an aqueous solution of alkali carbonate of anothercomposition than the aforementioned composition is used, the manganesedioxide produced is in small, square and irregular crystal form and hasa diameter of several microns or 30 microns in the maximum, no matterhow its concentration, temperature and rate of pouring may be changed.The manganese dioxide of such poor quality only has a low rate ofapparent charge density of 0.8 to 1.3 g./cc.

When the aqueous solution of alkali carbonate according to thisinvention is used, the same results can be achieved by replacing sodiumbicarbonate and ammonium bicarbonate with each other in part or wholly.For example, the aforementioned optimum range of proportion is stilleffective when a mixture of sodium carbonate and ammonium bicarbonate isused.

The reason why the temperature for causing precipitation of manganesecarbonate is limited to a range from room temperature to C. in thepresent invention is that it is possible to produce crystals ofmanganese carbonate of a high rate of apparent charge density rangingfrom 1.6 to 2.1 g./cc. if this temperature range is used for causingprecipitation, but that the crystals produced by heating to atemperature above 90 C. have a low rate of charge dentity of 1.0 to 1.3g./cc. If the temperature for causing precipitation is below roomtemperature, then it is required to effect cooling and this isuneconomical. Moreover, the crystals produced at a temperature belowroom temperature have a rather low rate of charge density.

The reason why the range of proportion of an aqueous solution of asoluble manganese salt and an aqueous solution of alkali carbonate inthe mixture is set at 120.9 to 111.2 in chemical equivalent is that thecrystals of manganese carbonate produced by using a mixture in thisrange are sufficiently large in size and have a sufficiently high rateof charge density. However, if the proportion of the two aqueoussolutions is below 110.9 or above 1:1.2, then the crystals of manganesecarbonate produced are square in shape and small in size and have a lowrate of apparent charge density. From the point of view of reducingproduction costs, the proportion of the two aqueous solutions ispreferably 1:1.

Another important feature of the method of this invention is that anaqueous solution of a soluble manganese salt and an aqueous solution ofalkali carbonate are mixed in a chemically equivalent ratio, by pouringseparately and simultaneously into a reaction vessel. It has hithertobeen customary to add an aqueous solution of alkali carbonate to anaqueous solution of a soluble manganese salt or to add an aqueoussolution of a soluble manganese salt to an aqueous solution of alkalicarbonate to cause them to react with each other. However, these methodsof the prior art have been unable to produce crystals of a sufficientlyhigh rate of charge .density no matter how carefully adjustments of theconcentrations of aqueous solutions, rate of pouring and the rate ofagitation are effected. lt

is only be pouring the two aqueous solutions separately andsimultaneously into a vessel and agitating the mixture according to themethod of this invention that crystals can be made to growsatisfactorily while maintaining the ions of manganese and carbonic acidin the mixture in equilibrium. This feature makes it possible carry themethod into practice as a continuous reaction system in which the twoaqueous solutions are continuously poured into a reaction vessel whilethe crystals formed and the mixture are withdrawn from the vesselthrough its lower end or other suitable portion.

It is necessary to thoroughly agitate the mixture of two solutions inproducing manganese carbonate. If the mixture is not agitated at all,then the crystals formed are mostly small in size. Accordingly, thecrystals produced have a low rate of charge density and cannot attainthe end of this invention.

It has been found that if the rate of formation of crystals byprecipitation is set at 5 to 800 grams for 1 liter of the mixture of twoaqueous solutions per hour, it is possible to produce manganesecarbonate in crystals which are sufficiently large in size and whichhave a sufiiciently high rate of charge density. If the rate of crystalformation is below 5 grams per hour, the process is not economicallyacceptable because the reaction vessel becomes too large in size as itis designed now. Conversely, if the rate is above 800 grams per hour, itis not possible to make the crystals grow sufficiently large, therebymaking it impossible to produce crystals having a high rate of chargedensity.

To sum up, it is possible to produce manganese carbonate in crystalswhich are sufficiently large in size and which have a high rate ofcharge density only when the reaction temperature, the composition ofalkali carbonate and the proportion of its components, the proportion oftwo aqueous solutions in the mixture, and the system of pouring the twoaqueous solutions into a vessel meet the conditions which constituteessential requirements of this invention. One characterizing feature ofthis invention is that it is only by subjecting manganese carbonatehaving a high rate of charge density to further processing operationsthat manganese dioxide having a high rate of charge density can beproduced.

ture below 300 C. or above 450 C., the MnO content of crude manganesedioxide produced by heating manganesecarbonate for 12 hoursconsecutively in atmosphere air is less than 40 percent. The Mn0 contentis increased only by several percent above this level even if causticalkali is added to the manganese carbonate under processing and heatingis continued for an additional 5 hours. It is not economical to use forfurther processing the crude manganese dioxide produced by heating attemperatures which are not in the aforementioned optimum range. That is,it requires a high acid consumption when treated with acids in the nextoperation. Moreover, the manganese dioxide produced as a final producthas a low activity and particularly its electomotive forceis low and itsdischarge time is short when used with dry cells. Thus, the temperatureat which manganese carbonate is heated in atmosphere air in the methodof this invention is limited to 300 to 450 C.

The invention calls for the process of heating manganese carbonate to arange from 280 to 400 C. in an atmosphere containing 10 to 80 percent byvolume of water vapor which is g a feature characteristic of thisinvention. It has been found that this process permits the production ofmanganese dioxide of high quality in a short interval of time. The crudemanganese dioxide produced by this process naturally requires a smalleramount of acids in the next operation. In addition, a reactor of smallercapacity can be used. Table 1 presents the results of experiments onMnO, contents of crude manganese dioxide produced from manganesecarbonate by pyrolysis and oxidation by heating in an environmentcontaining water vapor according to this invention and by heating merelyin atmosphere air.

The figures in the block in Table 1 refer to the MnO, contents of crudemanganese dioxide produced by heating manganese carbonate attemperatures in the range according to this invention in an atmospherecontaining water vapor. It will be seen that it is possible to increasethe MnO content of manganese dioxide to over 60 percent by heatingmanganese carbonate for 6 hours if the range of temperature according tothis invention is used. If the conditions are carefully adjusted,

TABLE 1 MnOz contents of crude manganese dioxide Heating atmosphere(vol. percent) 250 C. 6 hrs. later 280 C. 6 hrs. later 350 C. 3 hrs.later 400 C. 6 hrs. later 450 C 6 his. later 6 hrs. later The operationof producing crude manganese dioxide from manganese carbonate bypyrolysis and oxidation will now be explained. Several processes havehitherto been proposed for effecting pyrolysis and oxidation ofmanganese carbonate. They include the process of heating manganesecarbonate at 300 to 450 C. in atmosphere air, for example. The crudemanganese dioxide formed by this process may be added with 5 to 25percent caustic alkali and heated again to 300 to 450 C. so as therebyto increase the MnO content of the product.

In the method of this invention, the aforementioned process of the priorart is used to produce crude manganese dioxide which is furtherprocessed to provide manganese dioxide of high quality and highefficiency suitable for use with dry cells. The reason why thetemperature at which manganese carbonate is heated in atmosphere air islimited to a range from 300 to 450 C. is set forth hereinafter. Whenmanganese carbonate is heated in atmosphere air, crude manganese dioxideproduced by heating at 300 to 450 C. for 7 to 8 hours has a MnO contentof 60 to 70 percent. Crude manganese dioxide produced by heating at 300to 450 C. for 9 hours after adding caustic alkali to manganese carbonatehas a MnO content of about 75 percent. If heating is effected at atemperait would be possible to increase the MnO, content of manganesedioxide to nearly percent by heating manganese carbonate for only 3hours or to over 80 percent by heating manganese carbonate for 6 hoursat temperatures in the range according to this invention.

It will be seen from the table that substantially the same results areobtained in Mn0 content when heating is effected in an atmospherecontaining less that 10 percent by volume of water vapor and whenheating is effected in atmosphere air, the MnO content of the manganesedioxide produced in both cases being relatively low. On the other hand,they MnO, content of manganese dioxide produced by heating in anatmosphere containing over percent by volume of water vapor is markedlyreduced. When an atmosphere contains 10 to 80 percent by volume of watervapor, the Mn0 content of manganese dioxide produced by heating at atemperature below 280 C. or above 400 C. is markedly reduced. It isbased on the results of experiments listed in Table l and discussed indetail hereinabove that the conditions for heating manganese carbonatein an atmosphere containing water vapor are limited to temperatures in arange 280 to 400 C. and 10 to 80 percent by volume of water vapor in themethod according to this invention.

The operation of producing manganese dioxide of high quality from crudemanganese dioxide will now be explained. This operation involves causingcrude manganese dioxide to be impregnated with dilute or concentratedsulfuric acid and heated or causing the same to be impregnated withnitric acid and heated so as thereby to produce manganese dioxide ofhigh MnO content.

The crude manganese dioxide produced by the operation described abovecontains unreacted MnCO; and MnO in its particles because it is obtainedfrom manganese carbonate by pyrolysis so that its MnO content is low.When such manganese dioxide is used with dry cells, its dischargecapacity is low. The end of providing manganese dioxide of highdischarge capacity and high Mn0 content adapted for use with dry cellscan be attained by causing crude manganese dioxide to be impregnatedwith dilute or concentrated sulfuric acid and heated to effectextraction. The sulfuric acid used in this operation has a range ofconcentrations from 40 to 80 percent. lt has been found that heating ofcrude manganese dioxide at 50 to 1 C. after causing the same to beimpregnated with sulfuric acid of this concentration range markedlyincreases the discharge capacity of manganese dioxide when used with drycells. It has also been found that when the concentration of sulfuricacid is below 40 percent or the temperature at which heating is effectedis below 50 C., extraction of MnO which does not concern in discharge isnot effected satisfactorily, and that when the concentration of sulfuricacid is over 80 percent or the temperature at which heating is effectedis over 110 C., the manganese dioxide produced after this processing ismade inactive. Thus, the manganese dioxide produced under conditionsother than those of the present invention stated above has a smalldischarge capacity when used with dry cells.

The present invention calls for causing crude manganese dioxide to beimpregnated with dilute or concentrated nitric acid in place of beingimpregnated with dilute or concentrated sulfuric acid. This treatmentproduced manganese nitrate from divalent manganese. When subjected topyrolysis, manganese nitrate produces manganese dioxide which fills thepores in the particles of crude manganese dioxide, thereby increasingthe apparent density of manganese dioxide. This also eliminates orminimizes divalent manganese in amount which might otherwise be freed byelution. 1n the operation according to this invention, crude manganesedioxide is caused to be impregnated with dilute or concentrated nitricacid in an amount which is 0.5 to 1.5 times as much as the amount ofdivalent manganese, preferably 0.8 to 1.0 time as much as the amount ofdivalent manganese, contained in the crude manganese dioxide.Preferably, the nitric acid used in this operation has a concentrationwhich is in the range from 30 to 98 percent. The use of nitric acid ofconcentrations outside of this range is not desirable. It has been foundthat if the concentration of nitric acid is below 30 percent, divalentmanganese contained in crude manganese dioxide is introduced into thesolution by elution, and that if the concentration is above 98 percentas is the case with fuming nitric acid, N0 in the nitric acid is lost inthe next heating operation. Thus, the use of nitric acid of higherconcentration entails a loss of material and higher expenses.

It has been found that when crude manganese dioxide is caused to beimpregnated with nitric acid, the maximum amount of a nitric acidsolution that can be used with no adverse efiect is 35 cubic centimetersper 100 grams of crude manganese dioxide. The use of nitric acid inamounts greater than this maximum amount is not desirable because itcauses elution of manganese nitrate formed by reaction, therebyincreasing the loss of material.

The reason why limits are set to the amount of nitric acid used is setforth hereinafter. When the amount of nitric acid is less than 0.5 timeas much as the amount of divalent manganese in crude manganese dioxide,it is not possible efiectively to fill the pores in the particles ofcrude manganesedioxide with manganese dioxide even if heating isefiected in the next following operation. If the amount is increased toover 0.5 time as much as the amount of divalent manganese in crudemanganese dioxide, then the apparent density is rapidly increased untilthe amount reaches a level of 0.8 to 1.0 time as much as the amount ofdivalent manganese in' crude manganese dioxide at which the effect offilling the pores of crude manganese dioxide and thereby increasing itsapparent density can be increased to the maximum. The use of nitric acidin amounts above 1.5 time as much as the amount of divalent manganese incrude manganese dioxide is not desirable because additional energy isrequired in the next following pyrolysis operation and the device usedfor recovering nitric acid must be increased in scale, so that the useof a larger amount of nitric acid than the upper limit of the rangeaccording to this invention is uneconomical. Therefore, the optimumrange of the amounts of nitric acid is from 0.5 to 1.5 times as much asthe amount of divalent manganese in crude manganese dioxide.

According to the method of the present invention, the crude manganesedioxide impregnated with nitric acid is heated at temperature range from40 C. to the boiling point temperature of nitric acid in order that thenitric acid taken up by crude manganese dioxide and divalent manganesemay fully react with each other and to prevent the local escape ofunreacted nitric acid caused by sudden heating in the next pyrolysisoperation.

The crude manganese dioxide heated as aforementioned is heated again to160 to 300 C. by means if a tunnel kiln or other suitable heatingfurnace. As a result, the manganese nitrate disposed in the pores ofcrude manganese dioxide undergoes decomposition and the pores are filledwith manganese dioxide produced as the result of decomposition ofmanganese nitrate. Thus, manganese dioxide of high MnO, content and highapparent density is produced. The reason why the temperature at whichheating is effected is limited to the range from 160 to 300 C. is setforth hereinafter. It has been found that if the temperature is below160 C., the decomposition of manganese nitrate does not take place atall, and that if it is over 300 C., the manganese dioxide produced haspoor discharge characteristics. Thus, the optimum range of temperaturesat which heating is effected according to this invention is limited tothe range from 160 to 300 C.

It should be understood that the manganese dioxide produced by theaforementioned processing operations is, of course, made into asuspension in 30 to percent sulfuric acid, heated, filtered, and thenwashed with water by the usual process in order to further increase thequality of product and activate it. Moreover, the pH of the manganesedioxide may be adjusted because it contains traces of acid even if it iswashed with water, so that the residual acid may be neutralized and a pHbuffer may be provided to this manganese dioxide. To attain the end, themanganese dioxide produced is immersed in an aqueous solution of severalpercents sodium bicarbonate and ammonium chloride. After having its pHadjusted, the manganese dioxide is filtered and dried by heating at atemperature below C. to provide a final product.

The method provided by this invention has been explained in detail. Itshould be noted that the invention permits the production of manganesedioxide of high apparent density and high MnO content without reducingits activity and deteriorating its discharge capacity and otherelectrical properties. The method according to this invention offersadvantages in that costs for chemicals and treatment are reduced and theapparatus required for carrying the method into practice can be madesmaller in scale than conventional apparatus.

The examples of carrying the method of this invention into practice willnow be described.

EXAMPLE 1 ZN-MnSO, was produced from manganese carbonate by extractionwith sulfuric acid refined by removing iron and heavy metals therefrom.MnSO and a mixture of (NH CO and Nl-lJ-lCO were poured separately andsimultaneously into a manganese carbonate precipitation tank at rates of50 liters per hour and 100 liters per hour from a tank containing 1,500

liters of a solution of ZN-MnSO and a tank containing 3,000 liters of asolution of 0.8N-(NH CO and 0.2N-NH HCO respectively. Said manganesecarbonate precipitation tank, which has a capacity of 2,000 liters andwhich is provided with two an agitator of 2 HP, was placed below theaforementioned two tanks, with 200 liters of lN-(NH SO adjusted to a pH7 being placed in the precipitation tank beforehand. The two solutionswere poured into the precipitation tank such that they were separatelyintroduced into a large quantity of solution in the tank to be scatteredtherein and then mixed together without being mixed together instantlyafter'pouring. The positions at which the two solutions are poured intothe precipitation tank and the manner of agitating the solutions wereadjusted to serve the aforementioned purpose. Manganese carbonate wasproduced by precipitation after the mixture was allowed to stand in thetank at C. for 20 hours.

In order to maintain the liquid level in the precipitation tankconstant, a liquid containing no sediment was taken out constantly fromthe tank by means of a vacuum filter. Samples of small quantities weretaken out at regular intervals and the crystals were dried after washingwith water. The MnCO in the liquid after 20 hours had a concentration of600 grams per liter. The crystals formed had a rate of apparent chargedensity of 2.04 grams per cubic centimeter. The crystals were roundishin shape, with an average diameter of 70 microns. The manganesecarbonate produced as aforementioned was filtered and dried at 90 C.

500 kilograms of the manganese carbonate was placed in an horizontalcylinder 3,000 millimeters in length and 1,000 millimeters in diameterand having a built-in shaft mounting agitation blades and rotating at 10rpm, and air preheated to 320 C. and containing 40 percent by volume ofwater vapor was introduced into said horizontal cylinder at a rate of0.35 cubic meters per minute so as to heat the manganese car- 35 bonateat 300 to 320 C. for 5 hours. The composition by weight of crudemanganese dioxide produced was as follows:

MnO

T-Mn

MnO,

The crude manganese dioxide had a rate of apparent charge density of1.62 grams per cubic centimeter.

44 parts of 60 percent nitric acid was gradually added to 100 parts ofthe manganese dioxide of aforementioned composition and they wereagitated and mixed to provide wet par- 45 ticles having no liquid phaseto all appearance. The particles were allowed to stand at 100 C. for 15minutes and then heated at 200 C. for 1 hour in an electrically heatedtunnel kiln to provide 98 parts of manganese dioxide having a Mn0content of 89.2 percent and a rate of apparent charge density 5 of 1.71grams per cubic centimeter.

The manganese dioxide produced was placed in 100 parts of 48 percentsulfuric acid and agitated while heating at 80 C. for 1 hour so as toproduce a suspension of manganese dioxide in sulfuric acid. After beingfiltered and washed with warm water of C., manganese dioxide was placedin 85 parts of a pH adjusting solution comprising by weight 100 parts ofwater,

5 parts of sodium bicarbonate and 2 parts of ammonium chloride andagitated while heating at 60 C. for 20 minutes to 60 produce asuspension of manganese dioxide in the pH adjusting solution. Then,manganese dioxide was filtered again and dried at 80 C. for 2 hours. Themanganese dioxide produced had a composition which was as follows (byweight):

MnO

T-Mn

MnO, 91.8

process described with reference to Example 1 were placed in MnO T-Mn59.5

MnO 76.3

The manganese dioxide had an apparent charge density of 1.60 grams percubic centimeter.

75 parts of 75 percent nitric acid was gradually added to 100 parts ofthe manganese dioxide of aforementioned composition and they wereagitated and mixed to provide wet particles which were heated at 100 C.for 15 minutes and then at 200 C. for 90 minutes to provide 100 parts ofmanganese dioxide with a MnO content of 86.8 percent and a rate ofapparent charge density of 1.66 grams per cubic centimeter.

The manganese dioxide produced was placed in 100 parts of 48 percentsulfuric acid and agitated while heating at C. for 1 hour to produce asuspension of manganese dioxide in sulfuric acid. After being filteredand washed with warm water of 60 C., the manganese dioxide was placed inparts of the same pH adjusting solution as described with reference toexample 1 and agitated while heating at 60 C. for 20 minutes to producea suspension of manganese dioxide in the pH adjusting solution. Then,the manganese dioxide was filtered and dried at 80 C. for 2 hours. Themanganese dioxide produced had a composition which was as follows (byweight):

MnO

The manganese dioxide produced as a final product had a very high rateof charge density of 1.7l grams per cubic centimeter. It hadsubstantially the same discharge capacity as the manganese dioxide ofexample 1 when used with dry cells.

EXAMPLE 3 parts of crude manganese dioxide produced by the processdescribed with reference to Example 1 and having the composition showntherein was placed in 90 parts of 60 percent sulfuric acid and agitatedwhile heating at 70 C. for 1 hour to provide a suspension of manganesedioxide in sulfuric acid. After being filtered and washed with warmwater of 60 C., the manganese dioxide was placed in the same pHadjusting solution as used in Example 1 and agitated while heating at 060 C. for 20 minutes to provide a suspension of manganese T-Mn MnO, 90.7

MnO

The manganese dioxide produced as a final product had a rate of apparentcharge density of 1.69 grams per cubic centimeter. It had substantiallythe same discharge capacity as the manganese dioxide produced by theprocess described with reference to Example 1 when used with dry cells.

What is claimed is:

1. A method of producing manganese dioxide comprising the steps of a.pouring an aqueous solution of a soluble manganese salt and an aqueoussolution of alkali carbonate separately and simultaneously into areaction vessel and gradually mixing the two solutions by agitating at acrystal precipitation temperature ranging from room temperature to 90 C.so that the two solutions may react with each to produce manganesecarbonate, said aqueous solution of alkali carbonate being selected fromthe group consisting of (1) sodium carbonate and sodium bicara: no

9 bonate in a range of propo rnon of 6:4 to 1 (Ta n d 2 )ammoniumcarbonate and ammonium bicarbonate in a range of proportion of 9.6204 to0:10;

b. heating the manganese carbonate produced by the preceding step to 280to 400 C. in an atmosphere containing to 80 percent by volume of watervapor to produce crude manganese dioxide having an apparent rate ofcharge density of above 1.6 grams per cubic centimeter; and

c. causing the crude manganese dioxide produced by the preceding step tobe impregnated with dilute or concentrated nitric acid in an amountwhich is 0.5 to 1.5 times as much as the divalent manganese contained insaid crude manganese dioxide, heating the crude manganese dioxideimpregnated with nitric acid at a temperature range from 40 C. to theboiling point temperature of nitric acid, followed by further heating toa range from 160 to 300 C. to produce manganese dioxide.

2. A method of producing manganese dioxide which comprises the steps ofa. pouring an aqueous solution of a soluble manganese salt and anaqueous solution of alkali carbonate separately and simultaneously intoa reaction vessel and gradually mixing the two solutions by agitating ata crystal precipitation temperature ranging from room tempera ture to 90C. so that the two solutions may react with each other to producemanganese carbonate, said aqueous solution of alkali carbonate beingselected from the group consisting of (1) sodium carbonate and sodiumbicarbonate in a range of proportion of 6:4 to 0:10 and (2) ammoniumcarbonate and ammonium bicarbonate in a range of proportion of 9.6204 to0: 10;

heating the manganese carbonate produced by the preceding step to 300 to450 C. in atmosphere air after adding an aqueous solution of an alkalisuch as caustic soda, caustic potash or the like to produce crudemanganese dioxide having an apparent rate of charge density of above 1.6grams per cubic centimeter; and

c. Causing the crude manganese dioxide produced by the preceding step tobe impregnated with dilute or concentrated nitric acid in an amountwhich is 0.5 to 1.5 times as much as the divalent manganese contained insaid crude manganese dioxide, heating the crude manganese dioxideimpregnated with nitric acid at a temperature range from 40 C. to theboiling point temperature of nitric acid, followed by further heating toa range from 160 to 300 C. to produce manganese dioxide.

3. A method of producing manganese dioxide comprising the steps of a.pouring an aqueous solution of a soluble manganese salt and an aqueoussolution of alkali carbonate separately and simultaneously into areaction vessel and gradually' mixing the two solutions by agitating ata crystal precipitation temperature ranging from room temperature to 90C. so that the two solutions may react with each other to producemanganese carbonate, said aqueous solution of alkali carbonate beingselected from the group consisting of (1) sodium carbonate and sodiumbicarbonate in a range of proportion of 6:4 to 0:10 and (2) ammoniumcarbonate and ammonium bicarbonate in a range of proportion of 96:0.4 to0:10;

b. heating the manganese carbonate produced by the preceding step to arange from 280 to 400 C. in an atmosphere containing 10 to percent byvolume of water vapor to produce crude manganese dioxide having anapparent rate of charge density of above 1.6 grams per cubic centimeter;and

c. Adding 40 to 80 percent concentrated sulfuric acid to the crudemanganese dioxide produced by the preceding step and heating the crudemanganese dioxide to 50 to 1 10.

C. so as thereby to remove divalent manganese by elution, thus producingmanganese dioxide of high MnO content.

2. A method of producing manganese dioxide which comprises the steps of a. pouring an aqueous solution of a soluble manganese salt and an aqueous solution of alkali carbonate separately and simultaneously into a reaction vessel and gradually mixing the two solutions by agitating at a crystal precipitation temperature ranging from room temperature to 90* C. so that the two solutions may react with each other to produce manganese carbonate, said aqueous solution of alkali carbonate being selected from the group consisting of (1) sodium carbonate and sodium bicarbonate in a range of proportion of 6:4 to 0:10 and (2) ammonium carbonate and ammonium bicarbonate in a range of proportion of 9.6:0.4 to 0:10; b. heating the manganese carbonate produced by the preceding step to 300* to 450* C. in atmosphere air after adding an aqueous solution of an alkali such as caustic soda, caustic potash or the like to produce crude manganese dioxide having an apparent rate of charge density of above 1.6 grams per cubic centimeter; and c. Causing the crude manganese dioxide produced by the preceding step to be impregnated with dilute or concentrated nitric acid in an amount which is 0.5 to 1.5 times as much as the divalent manganese contained in said crude manganese dioxide, heating the crude manganese dioxide impregnated with nitric acid at a temperature range from 40* C. to the boiling point temperature of nitric acid, followed by further heating to a range from 160* to 300* C. to produce manganese dioxide.
 3. A method of producing manganese dioxide comprising the steps of a. pouring an aqueous solution of a soluble manganese salt and an aqueous solution of alkali carbonate separately and simultaneously into a reaction vessel and gradually mixing the two solutions by agitating at a crystal precipitation temperature ranging from room temperature to 90* C. so that the two solutions may react with each other to produce manganese carbonate, said aqueous solution of alkali carbonate being selected from the group consisting of (1) sodium carbonate and sodium bicarbonate in a range of proportion of 6:4 to 0:10 and (2) ammonium carbonate and ammonium bicarbonate in a range of proportion of 9.6:0.4 to 0:10; b. heating the manganese carbonate produced by the preceding step to a range from 280* to 400* C. in an atmosphere containing 10 to 80 percent by volume of water vapor to produce crude manganese dioxide having an apparent rate of charge density of above 1.6 grams per cubic centimeter; and c. Adding 40 to 80 percent concentrated sulfuric acid to the crude manganese dioxide produced by the preceding step and heating the crude manganese dioxide to 50* to 110* C. so as thereby to remove divalent manganese by elution, thus producing manganese dioxide of high MnO2 content. 